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Mathematics and Statistics Skills

Spotting weaknesses in how data is presented

  • 3 things to know
  • All three papers

Overview

Selective figures, axes that start above zero or use uneven intervals, short runs of records, unchecked sources, misleading pictorial symbols, averages without spread, percentages without totals, small samples and shading bands.

What you need to know

Answer each one before you reveal it.

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Key term

What is meant by a selective presentation of figures?

Key term

How can the vertical axis of a chart be used to mislead?

Evaluation

What weakness follows from a small sample?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is meant by a selective presentation of figures?

    Model answer

    Showing only the numbers that support a particular case and leaving out those that would weaken it.

  2. 2

    How can the vertical axis of a chart be used to mislead?

    Model answer

    By beginning it well above zero, which makes small differences between the columns look far greater than they really are.

  3. 3

    Why are uneven intervals along an axis a fault?

    Model answer

    They stretch one part of the data and squash another, so the shape of the graph no longer matches the numbers behind it.

  4. 4

    Why is a short run of records a weakness in an argument about change?

    Model answer

    Because a handful of years cannot show whether a change is a lasting trend or just an ordinary fluctuation.

  5. 5

    Why should the source and the date of a set of figures always be checked?

    Model answer

    Because old figures may no longer be true, and an organisation with an interest in the outcome may have chosen which numbers to release.

  6. 6

    Why is a symbol shown twice as tall to represent double a value misleading?

    Model answer

    Making it twice as tall usually makes it twice as wide as well, so it covers about four times the area for a value that has only doubled.

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